1. Field of the Invention
The present invention relates to the field of LED light bulbs, and more particularly to an axially symmetric LED light bulb with the features of high light uniformity and wide-angle illumination range.
2. Description of the Related Art
LED with the features of high efficiency, high color rendering, environmental friendliness, energy saving and long service life is used generally used as a light source for various illumination lamps.
For example, the conventional light bulb at an early stage uses a tungsten filament as the light source, wherein electricity is passed through the tungsten filament, and the tungsten filament is heated to incandescence to emit light for the illumination purpose due to the resistance of the tungsten filament. The light emission of such light bulb is similar to that of a light source, so that when such light bulb is used for illumination, a luminous efficacy of 360-degree full-circumferential radiation is achieved. A s described above, LEDs are used extensively as a light source for lamps, but most of the light sources in the present LED light bulbs are designed with a light emitting surface facing upward and perpendicular to the light emitting angle. In the meantime, the shape and structure of the light bulb provides a screening effect to the light, so that the light emitting angle of the conventional LED light bulb is usually not too large, and the light is too concentrated and comes with a narrow light emitting angle. With the aforementioned restrictive properties including the light emitting angle and the total light lumen of the LED, the conventional LED light bulb is unable to achieve the full-circumferential uniform illumination effect like the conventional incandescent lamps with the feature of a uniform wide-angle light emission. Therefore, the conventional LED light bulb still requires improvements of the illumination angle and the uniformity of light to achieve a better illumination performance of the LED light bulb.
To improve the luminous efficacy of the LED light bulb, most manufacturers adopt a 3D light source to increase the illumination angle of the LED light bulb, such that the LED light bulb can achieve the effect of a full-circumferential illumination similar to that of the tungsten filament. With reference to FIGS. 1 to 4 for various types of conventional LED light bulbs 1 available in the market, the LED light bulb 1 adopts an LED light source 10 arranged in a vertical direction, such that the light output angle of the light emitted from the LED light bulb 1 may be increased. In FIG. 2, the LED light bulb 1 also adopts a vertically arranged LED light source 10. Compared with the LED light bulb 1 as shown in FIG. 1, the LED light bulb 1 as shown in FIG. 2 uses a greater number of LED light sources 10, so that a 3D light source with more surfaces produces and outputs more lights in different angles. In FIG. 3, the LED light bulb 1 is assembled by using a multi-angle circuit substrate 1, such that the lights of the LED light sources 10 may be emitted to different angles. In FIG. 4, a secondary optical lens 12 is added to the top of the LED light source 10 to achieve the effects of increasing the illumination angle and providing the full-circumferential radiation. However, the aforementioned method is commonly adopted in the LED light bulb with a light emitting surface facing upward, and it is necessary to design and consider the LED light source 10 again or even re-design the area for installing the LED light source 10 whenever the installation direction of the LED light source 10 is adjusted. In the LED light bulb 1 as shown in FIG. 1, there are just two areas for installing the LED light source 10, and thus there still exists an illumination angle unreachable by light. In the LED light bulb 1 as shown in FIGS. 2 and 3, such LED light bulb 1 is the present common 3D light source design. To improve the light output angle of the LED light source 10, it is necessary to increase the quantity of LED light sources 10, so that the quantity of lead frame or circuit substrates 12 for installing the LED light source 10 is increased accordingly, and the manufacturing and assembling costs are increased significantly. Although the light source is a 3D light source, the shape of the aforementioned LED light bulb 1 affects the light emitting angle of the LED light source 10, so that different LED light bulbs 1 require the lead frame or circuit substrates 11 which are designed one by one to comply with the required light output angle. In FIG. 4, some manufacturers adopt the method of installing an additional secondary optical lens 12 outside the LED light source 10, such that the illumination angle of the light is increased by the secondary optical lens 12. However, this method requires the installation of other components to the LED light bulb 1, and thus the manufacturing cost and assembling time are increased.
Therefore, the present methods adopted for improving the light output angle and uniformity of the LED light bulb increase the manufacturing cost, the assembling time and the level of difficulty of the design. Although these methods may overcome the issue of a low luminous efficacy of the LED light bulb, yet they still have the following drawbacks. Therefore, the inventor of the present invention provides an axially symmetric LED light bulb in hope of overcoming the drawbacks of the conventional LED light bulb and improving the illumination angle and light uniformity of the LED light bulb with planar light emission to omit the complicated design of the light source and lower the production cost.